It is known in the art that fuel injector performance can vary as a function of both on-time and rail pressure. This variance from nominal injector performance is a result of such factors as the machining tolerances of fuel injector components. In addition, these fuel injector performance deviations can change over the life of the fuel injector.
For instance, fuel injectors typically exhibit changes in their performance characteristics after an initial period of use. In particular, fuel injectors tend to experience an increase in the amount of fuel injected over a range of operating conditions after this breaking-in period. While this change in injection characteristics does not render the fuel injectors, or the engine into which they are incorporated, unfit for use, it can contribute to performance inconsistencies. For example, in engines utilizing smoke limiting maps, fuel injector limiting maps are used to limit the amount of fuel injected by fuel injectors during certain operating conditions to reduce undesirable engine emissions. However, when the fuel injectors are not performing in a manner that is consistent with the stored fuel injector performance curves, effectiveness of these smoke limiting maps can be compromised.
Evaluation of fuel injector performance has been previously addressed in the art. For instance, one known method of evaluating fuel injector performance involves removing an engine from a vehicle and connecting it to a dynamometer. The engine is then operated for a number of cycles, with the performance of the fuel injectors being monitored while the dynamometer absorbs the engine load. While this fuel injector evaluation method has proven effective, it can be expensive and unrealistic for engine owners. In addition, because the engine must be removed from the vehicle, the test must be performed trained personnel, typically at a service center. Thus, ascertaining injector performance characteristics at any given time is problematic.
Another such method is taught by Thomas in U.S. Pat. No. 5,839,420, entitled System and Method of Compensating for Injector Variability and issued on Nov. 24, 1998. This method or system determines an appropriate calibration code for each injector based on the performance difference of the injector compared to a nominal fuel injector. A logic controller uses this calibration code to alter on times determined by the engine control unit, thus causing the injector to perform more like a nominal injector and a group of injectors to perform more uniformly.
The present invention is directed to overcoming one or more of the problems as set forth above.